Evolving grid dynamics such as climate change and the introduction of more distributed energy resources on the grid, like electric vehicles and solar, have presented new challenges for utilities. These challenges include power-grid integration, system stability, congestion, atypical power flows and energy storage gaps. With increased unpredictability, utilities have more need for low-cost, real-time monitoring and forecasting of supply and demand as well as agile, real-time management to realize truly smart grids.
For this reason, Consolidated Edison Co. of New York (Con Edison) has teamed up with General Electric (GE) & PROLEC-GE (P-GE), a GE joint venture, and PARC, a Xerox company, to learn how network transformers must evolve to perform in the 21st century. Con Edison is one of the largest investor-owned utilities in the U.S., with a highly redundant system of distribution linesand electrical equipment that is one of the most reliable in the world. To stay ahead of the curve, powering New York often requires adopting new technologies to improve system reliability and increase operational efficiency.
Transformer Monitoring
S&P Global reported that among the largest 25 utility segments by customer count in 2016, Con Edison — with 3.4 million customers in 2016 — reported the lowest system average interruption duration index without a major event day, at 19 minutes. Furthermore, the utility’s system average interruption frequency index was 0.36 and customer average interruption duration index was 1.92 hours in 2017 for its radial network.
Con Edison has systems to monitor transformer pressure, temperature, oil-level status and load data. While these systems have helped to reduce unanticipated failures and enable proactive replacement, they can cost approximately US$2300 per network transformer, or 5% to 10% of the cost of the network transformer. Aside from being costly, these traditional monitoring systems are not sufficiently robust. They do not provide real-time visibility into the condition of the transformers or accurate measurements on performance, and while rare, transformer failures have occurred. Such failures led to the use of lagging indicators, like oil sample analysis, that require field visits and laboratory testing.
New York’s unique density also can be challenging when it comes to maintenance. Many of Con Edison’s network transformers are in tight, underground busy street-side vaults with demanding field environments for monitoring. Climate impacts, such as increased temperatures and potential flooding, also threaten transformers. All these events are happening at a time when utilities are under greater pressure from customers and regulators to control costs and bill increases.
Optical Sensing
To fill these gaps, Con Edison is testing an optical sensor technology, developed with PARC and GE, that measures more parameters, which could better correlate to transformer health. Early results from the technology trial are encouraging.
This innovation arose from the desire of Con Edison and GE for a more cost-effective, reliable approach to managing transformers and other grid assets. The sheer volume of distribution transformers makes their reliability essential to customer service. More than 50 million units operate in North America and 1 million new units come on-line each year. A study by the Canadian Electricity Association reported that around 500,000 failures occur each year, including 1800 catastrophic failures that cost millions of dollars and cause more than 3 million hours of lost service for customers.
The method being tested by Con Edison and its partners uses optical-sensing systems to manage transformers through the industrial internet of things (IIoT). Such optical-sensing systems directly monitor critical, internal components in new units and retrofitted older transformers.
Integral to the advance are the embedding of hair-thin, multiplexed fiber-optic (FO) and other optical sensors, a high-resolution optical readout and advanced analytics. PARC has combined its FO sensor technology with intelligent algorithms to develop a system that provides accurate real-time measurement of internal transformer temperature changes, anomalies in vibrations, corrosion and other conditions that indicate a unit is degrading. The technology can enable more than 90% diagnostic and prognostic accuracy for asset health and state, with negligible false-alarm rates.
Manageable Cost, Greater Accuracy
Optical sensors offer high performance, low cost and suitability to the harsh high-voltage environment within a transformer. However, current cost of the optical readout units that interpret subtle wavelength shifts has limited the use and mass field deployment of optical sensors. The optical-sensing system developed in the Con Edison project sought to address the shortcomings of other commercially available solutions with a low-cost, field-deployable, reliable monitoring solution for transformers and other grid assets.
The team completed development and laboratory validation of the technology suite, which included customized low-cost optical sensors and model-based system analytics for monitoring transformers. The team embedded optical sensors on critical components in the latest GE Safe-NET network transformers and other existing GE models.
Significant design and manufacturing challenges were addressed in formulating a method for embedding the optical sensors within transformer components, such as core and coil elements, while maintaining transformer performance and monitoring sensitivity. The sensing system measured key internal parameters and monitored events with a high-resolution, high-frequency optical readout.
The team validated the data and results against other commercially available laboratory instruments at GE that are used traditionally for testing or qualification of new transformer designs. For instance, the developed optical partial-discharge monitoring capability was validated by a Doble LDS-6 reference instrument.
Commercial GE network transformers using the embedded FO sensing solution were built, tested and qualified per the IEEE C57.12.90 standard test code for liquid-immersed transformers and Con Edison specifications. The parameters the analytics suite monitored were validated across a range of scenarios at GE’s transformer manufacturing and testing facilities in Shreveport, Louisiana, U.S. As an example, the optically monitored temperature variations in overload testing for qualification were comparable to embedded thermocouple results from lab test transformers for qualifying thermal performance of a new core/coil design (that are not practical to integrate in commercial transformers for qualification or to be field deployed). Additionally, the team developed and tested a version of the technology that could be retrofitted into currently deployed and older network transformers.
PARC, GE and Con Edison have completed an initial field trial to demonstrate the benefits of the technology for remote monitoring through IIoT under Con Edison’s challenging grid deployment conditions. The temperature variations of the optical-sensing system monitored across the transformer tank in various environmental conditions have offered deeper insights into transformer behavior under field-deployment scenarios at Con Edison. Certain optical signal features show promise in detecting and diagnosing key events. Con Edison, GE, PARC, and now P-GE continue to pursue this promising technology.
Beyond The Field Trial
A full-scale implementation of the IIoT monitoring solution could enable remote monitoring not only of network distribution transformers but also other grid assets where existing monitoring systems are costly or limited. This approach also could provide systematic alerts for unsafe or unexpected events, resulting from the introduction of more distributed energy resources, for example. This would enable utility professionals to view real-time trends in asset conditions, so they could plan better for maintenance and management. As a result, they could improve grid performance dramatically, which in turn would accommodate distributed energy resources and other evolving grid market dynamics.
PARC and GE’s monitoring and diagnostics group, Product Manager Alfonso Ambrosone, and P-GE’s USA LLC, Engineering Manager, Nabi Almeida are currently are evaluating the creation of a commercial offering, building on the results from the first two phases of research. The objective is to provide a cost-appropriate solution, sufficiently robust for the tough operating conditions of the distribution environment. Technical and cost feasibility studies are in progress, prior to assessing customer interest. This trial in New York’s busy streets is a step toward achieving more reliable utility service and enhanced public safety at a lower cost.
Brad Kittrell ([email protected]) is an engineer in the distribution engineering equipment group for Consolidated Edison Co. of New York. He manages the application of analytics to the operation of Con Edison’s fleet of network transformers and provides guidance on their application of network transformer operation and maintenance.
Ajay Raghavan ([email protected]) is director of research, IoT sensors and services at PARC, a Xerox company. His team is focused on developing cutting-edge analytics and sensing technologies for reliable, safe and optimal life-cycle management of a broad spectrum of cyber-physical systems. His application areas of interest include systems in the energy, transportation, aerospace, defense and manufacturing sectors.
Malcolm Smith ([email protected]) is a senior technology engineer for PROLEC-GE. He is a patent co-author on the related patents. The team participating in the ongoing development of Optic Sensing technology consists of PROLEC GE USA LLC transformer manufacturing and GE Monitoring & Diagnostics. He has been associated with network transformers & voltage regulators since February 1999.
